Pseudo-C2-Symmetric Bimetallic Bissalen Catalysts for Efficient and Enantioselective Ring-Opening of meso-Epoxides

摘要

Bimetallic catalysts have been synthesised based on Jacobsens C2-symmetric bissalen ligand. They constitute the first examples of compounds with pseuodo-C2 symmetry, owing to the presence of two different metal ions. They have been investigated in the ring-opening of meso-epoxides by trimethylsilyl azide (TMSN3). Pseudo-C2-symmetric [CrIII?Co]bissalen complexes were the best in inducing ee (9394?%) in the ring-opened product of cyclohexene oxide by TMSN3 under solvent-free conditions, whereas a pseudo-C2-symmetric [CrIII?MnIII]-bissalen complex displayed the highest turnover frequency (183 h-1) but induced a lower ee (66?%). A broad substrate scope was displayed by a pseudo-C2-symmetric [CrIII?Co]bissalen catalyst: at 0.1 mol?% catalytic loading and under solvent-free conditions, it induced the highest ee to date in the ring-opened product of a range of different meso-epoxides by using TMSN3.